Method and apparatus for refining fibrous material for the production of pulp



Unlted States Patent 11113,547,356

[72] Inventor Arne Johan Arthur Asplund [56] References Cited Tykovasen Lidingo 3, Sweden UNITED STATES PATENTS [211 P 1,228,338 5/1917 Marks 241/275 1221 1 2,616,466 11/1952 Linder et al. 241/275x [451 Paemed 1970 2 980 350 4/1961 Le'eune 241/255x [321 2691'966 12/1954 11 man 241/260 33] Sweden y [3 I] No. 2468/67 Primary Examiner-James M. Meister Attorney-Eric Y. Munson [54] METHOD AND APPARATUS FOR REFINING FIBROUS MATERIAL FOR THE PRODUCTION OF PULP lo Chlms 11 Drawing Figs ABSTRACT: Method an apparatus comprising a drum pro- [52) US. 241/28, vided with a plurality of inclined radially extending blades or 24l/54, 24l/247, 24l/255, 241/260 wings which rotate rapidly within a surrounding cylinder [5]] Int. Cl 827k 9/00; which is provided with uneven or rough surfaces along the in- B020 23/02 terior wall thereof between which surfaces and blades the raw 9 [50] Field ofSearch 241/18, 28, material to be refined is subjected to frictional forces while 54, 247, 255, 260, 275, 276 being moved through the cylinder in a linear direction.

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METHOD AND APPARATUS FOR REFINING FIBROUS MATERIAL FOR THE PRODUCTION OF PULP BACKGROUND OF THE INVENTION The invention relates to grinding apparatus, particularly for refining pulp material derived from vegetable lignocellulose substance for the production of paper products and the like. The starting material, which in the case of wood, is reduced to a mass of chips before being subjected to one or more treatments to form a raw material or unrefined pulp which is not yet in suitable condition for the production of paper. This raw material comprises a mixture of wood fibers and/or other vegetable fibers and water and is generally referred to as grist, the main content of which is the solid material derived from the lignocellulose substances.

In conventional refiners, especially of the disc refiner type, the grist is mechanically rubbed between solid surfaces with the working surfaces in very close proximity to each other. In these conventional refiners or grinding apparatus, grist is introduced between two discs, both of which may be rotating, or only one may rotate, and the other stationary, adjacent their central portion. The pulp coming from the center of the discs is by centrifugal action forced from the revolving disc over the stationary disc, where such disc pattern is used, back and forth guided by a series of dams. In this manner the grist passes through an area of shear developed between the discs before it emerges from the grinding zone. Thus, the centrifugal power acts upon the grist with an outwardly increasing force.

The grinding distance betweenthe discs must be very nar row, usually 2 mills to 4 mills, for low consistency refining of pulp. This narrow space between the discs is necessary because the grist at this stage is mechanically treated to liberate and subdivide the individual fibers to produce a socalled fibrillation which enhances the surface properties of the fibers to provide adherence in finished paper. These fibers have a diameter of some hundreths of a millimeter. In the conventional disc refiners, including hollanders and Jordan mills, the grist treated therein has a relatively low fiber concentration, and consequently the spacing between the fixed grinding members must be extremely narrow so that the pulp particles or the fibers are firmly gripped between the grinding surfaces. In other words, the spacing between the grinding surfaces must approach the cross-sectional dimension of the individual fibers. Thus, direct contact between the metallic grinding surfaces often occurs in this conventional apparatus with consequent increased wear of the grinding members. Because of the fact that the grinding discs may have a diameter up to one meter, or larger, their adjustment with respect to each other requires extreme precision. The torque exerted upon the shaft supporting the discs is also an important factor to be taken into consideration in connection with these conventional disc refiners.

SUMMARY OF THE INVENTION The pastelike grist to be refined is introduced between the working surfaces of the drum and the cylinder and is propagated or propelled in wavelike fashion in rapid pulsating succession in small clumps accelerated by the blades, which rotate at a linear speed ranging between 15 to l meters per second, corresponding to 30 to 200 miles per hour, along the inner surface of the cylinder and then retarded by the undulations to a near stop. The crests of the waves of grist are then sheared off by the body of grist carried forward by the tips of the blade of the drum. As the mass of grist is pushed along in front of a blade, a plane of shear is created a short distance from the edge of the blade. The force exerted by the blades in a linear direction, which might be in the range of 5 to kg. per cm. depending upon the speed of the drum and some other controllable factors, causes the grist to become compacted to such a density that though friction forces induced in the grist rise to such intensity that the fiber bundles are not only broken up, but the primary layer of the tracheide is moreor-less rubbed off leaving the secondary layer exposed to immediate fibrillation with consequent improved fiber-to-fiber adhesion by hydrogen bonds in the finished paper. The separation of the fiber bundles or the tracheides into their primary and secondary layers according to the invention has no substantial effect on the fiber lengths, which in coniferous wood is about 2mm. to 3mm, or in some instances 3, 5-4mrn., and in deciduous wood about lmm. Thus, the forces created in the interior of the grist by the centrifugal action is directed along the plane of shear and not against the blades and/or the cylinder.

The distance between the solid surfaces of the rotary drum and the undulations or projections on the cylinder does not have to be less than 1 or 2 millimeters in order to generate the required surfaces of shear.

The grist according to the invention is subjected to a centripetal acceleration of the order of at least 100 G, preferably 300-1 ,000 G and some cases 1,500 G and, if needed, in certain instances, to 2,000 G or higher. Under the effect of such high centripetal acceleration forces, the grist becomes compacted to a density which reaches 0.5l.3 gram per cubic centimeter. This high centripetal acceleration rate also induces frictional forces in the direction of the shearing plane, i.e. a cylindrical surface or zone between the drum and the cylinder of the order from 100 grams per square centimeter to 10 kilograms per square centimeter.

The degree of breaking up of the fiber bundles in the grist by the friction or mechanical rubbing of the fibers against each other is dependent somewhat on the moisture ratio in the grist, as well as by the fibrous structure of the material processed.

The moisture component distributed in the grist is partly held by strong molecular forces (the moisture equilibrium content) and partly by capillary forces of the liquid film formed on the liberated surfaces of the particles.

The thickness of this film and its viscosity will be a determining factor on its lubricating effect, and this in turn will determine the subsequent frictional effect on the surface layers of the fibers.

Increased internal frictional work results, of course, in increased temperatures which may have some effect on the refining process according to the invention.

The surface tension properties of water, which have a viscosity that decreases with the temperature, will influence the effect of the lubricant" so as to allow the fibers to slide more easily along each other at higher temperatures. This might be one factor that determines the fibrilizing effect, which in turn explains the variation in strength characteristics of the paper which according to experiments increases when the refining process is carried out at lower ranges of temperature. Refining of the grist at high range temperatures appears to have a negative effect on the tear factor and breaking length of semichemical pulp.

l have found that the grist can be kept at a temperature of 50 C. or below, if the refining process is carried out under partial vacuum. At a total pressure of about mm. mercury, water will evaporate at a sufficient rate to maintain the grist at a temperature of 50 C.

The combined peripheral and radial movement of the grist relative to the inner surface of the cylinder produces no substantial friction against this surface, as it is smooth and may be highly polished. Thus, the wear on the surface is insignificant and does not have to be made of any hard metal but can be made of plastic material, such as Teflon. In case the surface should be rough in the beginning it will become polished 'by the grist. This will make it further apparent that the fibrillation is not, or only to an insignificant degree, produced as the result of contact with the fixed parts of the apparatus.

Furthermore, because of the low friction coefficient, the power consumption required for producing the gliding movement between the grist and the cylinder surface will be relatively low. I

U.S. Pat. No. 2,008,892, FIGS. l9 -22, may be referred to as an example of the prior art which discloses inserts to provide rough frictional surfaces.

It is, therefore, among the objects of the invention to induce frictional forces in the planes of shear of the grist itself of such intensity that the fibers will be mechanically rubbed against each other with such force that the primary layer or the tracheid of the fibers is rubbed ofi' leaving the secondary layer exposed to fibrillation with consequent enhancement of the fiber-to-fiber adhesion properties by hydrogen bonds in the finished paper. I

Another object is to provide a method and apparatus where the working surfaces operate with a much larger spacing between the moving surfaces.

Another object is to provide an apparatus which is subjected to less torsional stresses than the conventional disc refiners and requiring adjustment with a substantially lesser degree of precision.

A further object is to provide an apparatus in which contact between the metallic grinding surfaces is eliminated with consequent preservation of their shearing efficiency and increased operating life of the apparatus.

Other objects and advantages inherent in the invention will be apparent from the following description taken in conjunction with the accompanying drawings.

In the drawings:

FIG. 1 is a side view partly in section of a refiner according to the invention;

FIGS. 2 and 3 are sections taken respectively along the lines 2-2 and 3-3 of FIG. 1;

FIG. 4 is a partial section of FIG. 3 drawn to an enlarged scale;

FIGS. 5 and 5A are schematic views taken along the line 5-5 of FIG. 4;

FIG. 6 is a diagrammatic sectional view of a portion of the rotary drum drawn to an enlarged scale;

FIG. 6A is an enlarged diagrammatic view of the force exerted in the plane of shear on a wavelike clump as it is retarded in one of the stationary undulations on the interior surface of the cylinder surrounding the drum;

FIGS. 7 and 8 show two alternative modifications of the members which impart a linear movement to the grist through the apparatus; and

FIG. 9 is a partial cross-sectional view of a modification of the stationary part of the apparatus.

Referring to the drawing, the reference numeral 10 designates a stationary cylindrical drum which may comprise a plurality of horizontal sections which is supported on a frame which is anchored to a platform 14. The cylindrical drum I0 is longitudinally extended relative to its inner diameter. The ratio may be 3:! or greater. One end of the cylinder is provided with an extension in the shape of a neck 16 having an inlet opening 18 for the grist, which is to be refined in the apparatus. The neck 16 may be provided with one or more screw-shaped members 20 for the purpose of facilitating feeding the grist into the cylinder 10in a radial direction.

The opposite end of the cylinder is also provided with an extension in the form of a collar 22 which has an outlet opening 24 for the discharge of the treated material. The latter is conveyed further by means of the conveyor 26.

A substantially cylindrical rotary drum 28 is journaled in bearings 32, 34. The rotary drum extends coaxially with the stationary cylinder 10 and its extensions 16 and 22. A series of blades 36 are mounted circumferentially about the drum. These blades preferably are straight and are arranged parallel to each other along the linear direction of the drum. They extend radially from the surface of the drum and incline slightly rearwardly with respect to the direction of rotation of the drum as shown by the arrow 38 in FIG. 6. The end surfaces 40 of the blades may be perpendicular to their sides.

Segments 42 are arranged at the interior surface of the cylinder 10 along the length thereof. These segments may have a peripheral width of about one-eighth of a revolution and are mounted side by side and abut against and are held in place by the cylinder 10 by means of ridges or shoulders 44, 46 which form a series of channels or interspaces 48. The inner surface of the segments facing the drum 28 are provided with a series of undulations or grooves 50, which according to the embodiment shown in FIGS. 6 and 6A, are nonsymmetrical in longitudinal sections, in that the groove has a relatively long and substantially straight inclined portion 52 which merges with a shorter, sharply bent transition portion 54. Between each pair of grooves, the intermediate portions 56 keep the cylindrical shape of the segments.

At one location, preferably at the upper part of the cylinder 10, is a rail member 58 in place of a segment 42 (see FIG. 4) which has bent sides 60. This member 58 serves to support the means for assuring the linear progression or propagation of the grist through the length of the cylinder 10. In the embodiment shown'in FIGS. 55A this means comprises cams 62 arranged successively in line along the longitudinal extension of the cylinder. The cams 62, which substantially conform to the FIG. of an equilateral triangle, are each supported on their own individual pins 64, which can be adjusted from the outside to change the angle of inclination of the cam to the generatrix of the cylinder. For this purpose, the part 66 of the pins 64 which protrudes outside of the cylinder is provided with flattened surfaces for engagement with a tool so that the pins can be locked in a desired position by means of a nut 68.

The blades 36 in the inlet neck R6 to the cylinder 10 have a reduced diameter as will be seen in FIG. I, in order to provide room for the screw-shaped member 20. In the opposite end of the apparatus, the blades have inclined wings 70 which propel the refined pulp towards the discharge opening 24 in the bottom of the cylinder. A conduit 72 extends from the interior of the apparatus, which is connected with a suction device or a vacuum pump (not shown).

The grist is introduced into the apparatus together with water in a proportion of about 1:2 through the inlet 18 and is subjected to a revolving motion by the blades 36 in the neck 16 where the screw-shaped-members 20 feed it in a linear direction into the cylinder 10.

The grist is pushed into heaps or clumps 74 in front of the blades 36 as will be seen from FIG. 6 and is accelerated by the latter to a high peripheral speed. The grist particles become firmly compacted by the centrifugal force acting thereon. This compacting force increases in strength as the grist particles are flung outwardly by the blades acting thereon. In FIG. 6 this centrifugal force is shown by the power parallelogram by the vector 76. The centripetal acceleration may reach 100 times the force of gravity G and more. At the same time the grist particles are subjected to a force along the vector 78 which is perpendicular to the rearwardly inclining frontal surfaces 80 of the blades. The vector sum of these two forces is shown by the diagonal 82 which is exerted in a radial, outwardly inclining direction.

The radial outer end surfaces of the blades 36 are spaced a few millimeters from the surfaces 56 of the segments 42. The grist layer lying closest to the segments 42 is retarded by undulations or grooves 50 and comes to a near stop compared with the grist particles being pushed along by the blades. Thus, one portion of the grist layer is-forced in a radial outward direction along the downwardly slanting surface 52 and is then reversed in the sharp bend along the surface 54. This results in a wavelike pulsating movement as the grist is caught and kept temporarily stationary in the grooves while at the same time it is passed over by the blades 36. Thus, a plane or surface of shear is created a short distance in front of the blade as shown by the broken line 86 in FIG. 4. In this plane the fibers are subjected to such a violent rubbing action and to frictional forces of such intensity that the tracheids rub off and leave the secondary layer exposed to direct fibrillation which enhances the quality of the paper made from the thus refined pulp.

An important functional feature of the invention is that the grist is subjected to the centrifugal force produced by the rotating drum 28 and the blades 36 while it is being accelerated through the cylinder 10 in a linear direction. The latter movement is enhanced by the cams 62. As shown in FIG. 5, the cams are so adjusted that their longer side surfaces 88 meet and convey the grist in an axial or linear direction. It

is conceivable, however, that the earns 62 may be mounted in reversed position so that their shorter side surfaces 90 accomplish this purpose as will appear from FIG. 5A. The cams and the bent rail 60 are beyond the outer extremity surface of the blades 36 or from the plane or surface of the shear 86. According to the invention, the feed in a linear or axial direction takes place not only at the inlet to the cylinder 10, but also throughout the longitudinal extension thereof. The object of this to link the grist together in the radial direction so that it is moved in a linear or axial direction by the feed members.

The increased frictional energy exerted on the grist during its pulsating progression through the apparatus is accompanied by a proportional increase in temperature, which by reason of evaporation of water may reduce the moisture and fiber ratio in the grist. Such a change in moisture and fiber ratio may have some effects on the refining process but this change can easily be corrected by the addition of water.

If the refining process is carried out at atmospheric pressure, the temperature rises to about 100 C. unless a special cooling step is resorted to. This may be accomplished by introducing a cooling medium in the channels 48 formed between the cylinder wall and the segments 42. Cooling down to 100 C. becomes automatic by evaporation in the form of steam at atmospheric pressure.

It is also possible to limit the temperature of the grist to a temperature below 100 C. such as for example 50 C. or even lower by carrying out the refining process in partial vacuum. A temperature of 50 C. corresponds to a negative pressure of 90mm. Hg absolute and consequently the temperature of the grist can be maintained at this temperature by keeping the negative pressure within the aforementioned limit. A sourceof suction may be connected to the conduit 72 and the vacuum treatment may be carried out generally as disclosed in my copending application Serial No. 413,207, filed Nov. 23, 1964.

FIG. 7 shows a modification of the feeding mechanism in a linear or axial direction through the apparatus. According to this modification the feeding device 92 has the shape of a double ax with its shaft in the center, and defines arcuate working surfaces.

FIG. 8 shows a wedge-shaped feeding device with straight side surfaces.

The grooves or undulations 96 in the segments 42 may have a semiovular contour in transverse section as shown in FIG. 9 which merge with the intermediate flat portions 56 at substantially the same angle.

It is also conceivable the droplet-shape grooves shown in FlGS. 6 and 6A could be in reversed position so that the sharply bent portion will engage the grist first.

It should, of course, be understood that the foregoing specification is given by way of example and the inventive concept as disclosed herein may find a variety of expressions within the accompanying claims.

lclaim:

l. The method of refining grist in a grinding apparatus comprising a rotor surrounded by a stationary longitudinally extending cylinder, the rotor being provided with a series of radial blades adapted to convey the grist through the apparatus, and the cylinder being provided with an interior uneven surface, said method comprising:

a. subjecting a portion of the grist to a centrifugal acceleration substantially in a circular path to compact the grist particles;

b. retarding the portion of the grist layer between the cylinder and the ends of the blades of the drum with consequent movement thereof being restricted to a peripheral direction in a limited degree;

c. subjecting the retarded portions to radially acting movement components by the drum so as to create a shearing zone between the cylinder and the plane defining the horizontal linear movement of the grist by the drum which shearing zone is substantially circular in section; and

dary layers of the fibers with consequent improvement of their fibrillation.

2. Method according to claim 1 in which the grist is subjected to a centrifugal acceleration while being passed through the apparatus on the order of at least 100 times the force of gravity.

3. Method according to claim 1 in which the grist while being conveyed in a linear direction, axial movement components are imparted thereto by the drum during a portion of its revolution.

4. Method according to claim 1 in which the layers of the grist particles nearest the cylinder wall are caused to move intermittently in their radial and peripheral movement by the action of the drum upon the grist.

5. The method of refining grist in a grinding apparatus comprising a rotor surrounded by a stationary longitudinally extending cylinder which rotor and cylinder have surfaces between which the grist is subject to frictional forces, comprismg a. passing the grist in wavelike successive clumps in a pulsating linear direction through the apparatus;

b. subjecting the grist to a centrifugal force during its linear movement;

c. retarding a portion of the clumps during the linear movement;

d. shearing the crests of retarded portion in a shearing zone between the rotor and the cylinder; and

e. inducing frictional forces within the several clumps of sufficient intensity to separate the fibers into their primary and secondary layers with consequent enhancement of their fibrillation.

6. Method according to claim 5 in which the grist is passed through the apparatus at a linear speed ranging between 15 to 100 meters per second.

7. Apparatus for refining grist having a rotor and a longitudinally extending cylinder surrounding said rotor, the rotor being provided with a series of blades adapted to convey the grist through said cylinder and shear the same during its passage therethrough without contact between the blades and the fibers of the grist to separate the primary and seconthe cylinder wall, said apparatus comprising:

a. means on the interior wall of said cylinder to propagate the grist in wavelike successive clumps in a pulsating linear direction through the cylinder;

b. means on the interior surface of said cylinder for retarding a wavelike portion of the grist;

c. means for producing a plane of shear within the grist at a slightly spaced distance ahead of the blades in the linear direction of the movement of the grist for shearing off the retarded wavelike portion; and

d. means for compacting the remaining portion of the clumps and induce therein a frictional force of sufficient intensity to separate the fibers of the grist into their primary and secondary layers.

8. An apparatus for refining grist comprising:

a. a rotor having a series of radially extending inclined blades for conveying the grist through the apparatus;

b. a stationary longitudinally extending cylinder surrounding said rotor and having an axially extending uneven surface on the interior wall thereof;

c. the circular plane defined by the rotating blades and the uneven surfaces being substantially concentrical and being spaced from each other a distance which is a multiple of the diameter of the grist fibers; and

(1. adjustable propagating members on the interior wall of the cylinder adapted to produce a movement component in axial direction on the grist as it is being passed through the cylinder.

9. An apparatus according to claim 8 wherein a plurality of the propagating members is arranged successively in a row along the axial length of the cylinder.

10. An apparatus according to claim ii wh ei'ei ri th e propagating members are arranged on an axially extending rail. 

